Population and climate raise tropical cyclone risks

February 18, 2012 — andyextance

A boy at the site of his family's damaged house in the Bangladeshi coastal district Cox’s Bazar that was damaged by a tropical storm. When a tropical storm becomes a hurricane-speed cyclone, such houses are just washed away. Casualties are higher when the population is not aware of the coming of a cyclone. Tropical cyclones are expected to become less frequent but more intense with future climate change. Credit: amioascension/Flickr

The number of people threatened by tropical cyclones and the disasters they can cause will “greatly increase” over the next 20 years. And though climate change is predicted to increase tropical cyclones’ intensity, the world’s rapidly increasing population will play an even larger part in raising that risk. “Higher intensity will increase the number of people exposed,” explained Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment Program in Geneva, Switzerland. “However, we also show that the increase in population is the main trigger that will increase exposure. This finding is key because some governments may be tempted to delay actions to protect their population over uncertainties in climate change’s impact on tropical cyclones.”

This message is what Bruno and seven other Europe and US-based scientists have learnt while developing a new approach for determining the risks from such cyclones. Currently that risk is calculated from databases of reported past events in which the number of disasters caused by tropical cyclones has increased steadily over the past 40 years. However, the deaths those disasters cause has fluctuated up and down, falling from 357,000 in the 1970s to 174,000 in the 2000s. Perhaps more common disasters have been balanced out by people becoming much less vulnerable, the scientists suggest in a paper published in research journal Nature Climate Change. Or perhaps the increased number of disasters is just due to better recording, as TV and the internet becomes more widespread.

Risk reassessment

So Bruno’s team decided to look for a way to calculate risks from tropical cyclones that can’t be biased by improved access to information. “Our method consists of two steps,” Bruno said. “In the first step we make a map of where tropical cyclones have been and how intense they were over the last four decades. We relate each one to its reported financial losses, how many people, assets or crops were exposed and how vulnerable each of these was to destruction or death to set up a statistical model. Then we apply that model globally to give mortality and economic risk per decade and report trends in risk at national level from 1970 to 2030.”

Map showing distribution of hazard frequency and mortality risk from tropical cyclones for the year 2010. Credit: Nature Climate Change

Using this approach Bruno’s team estimated that in 2010, 1.53 billion people and $1.63 trillion in assets were in tropical cyclone-prone areas in 81 different countries and territories. From this, on average 133.7 million people and $1,901 billion are in the way of a cyclone each year. Without climate change, population growth alone would increase the average population exposed per year to 149.3 million by 2030. Climate change is expected to reduce how often cyclones happen but make them more intense. Taken together, the researchers estimate this would reduce how many people are in the way of cyclones in 2030 to 144 million people.

Double impact

Tropical Cyclone Nargis several days before reaching Myanmar (Burma) in 2008, whose official warning to its population was provided on page 15 of the newspaper The New Light of Myanmar. At least 138,000 people died in Myanmar in the "mega-disaster" that followed. Governance is an important factor in determining the risks from tropical cyclones, Bruno Chatenoux and his colleagues found. Credit: NASA

But the increased cyclone intensity those people are set to be exposed to will influence the risks they experience. For the most powerful cyclones, how many people and how much property is in the way plays an especially important role in the risk of death and damage. So, not only are more people in the way, more intense storms put that higher population at greater risk. The level of poverty and how well developed a political system is in a country also influence its overall risk. For example, while every country struggles to withstand the most intense cyclones, poor areas would be more likely to suffer heavy losses in less intense cyclones.

The scientists also showed which countries were most often affected by cyclones, and which countries had the largest proportion of its assets and people at risk. “Japan has the highest overall exposure, small islands like Guam have the highest share of their population and economy exposed to tropical cyclones,” Bruno explained. Ranking countries in this way means that they can be compared, so that the UN and development agencies know where needs the most help.

Bruno and his colleagues would now like to continue working to see what damage storms could cause as climate continues to change. That includes how sea level rise and related beach erosion can influence the effects from storm surges. “The potential role of ecosystems such as coral reefs and mangroves in mitigating these impacts is interesting,” he said. “So far, most of the efforts for protecting coastal infrastructures and population are mostly based on engineering solutions, whereas we don’t know how much we can do by protecting or restoring ecosystems. Ecosystems also provide extra benefits like diving sites, fisheries, biodiversity, appealing scenery and carbon storage, which engineering doesn’t provide.”

All the data that Bruno’s team generated can be seen and downloaded through their PREVIEW Global Risk Data Platform. Non-profit organizations can freely download data, while others can get data credits.

2 Responses to “Population and climate raise tropical cyclone risks”

[…] long time periods that might be ideal. For example, this previously limited our understanding of global warming’s effect on tropical cyclones, Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment […]

[…] threatened by tropical cyclones and the disasters they can cause over the next 20 years. So said research published in February by Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment Program in Geneva, […]